Common chemical offers energy storage hope

Monday, 1 July 2013 Stephen PincockABC

Watts with titanium: Materials made out of titanium dioxide could store enormous amounts of energy, opening the door for innovation in the areas of renewable energy, electric cars, even space and defence technologies(Source: pedrosala/iStockphoto)

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Future potential A chemical found in everything from tennis court lines to low-fat milk could also help store energy produced by renewable sources, Australian scientists say.

The chemical, called titanium dioxide, is widely used as a whitening pigment in toothpastes, plastics, sunscreens and many more applications.

Chemist Yun Liu, an Associate Professor at the Australian National University (ANU), has also discovered that it may be useful for building energy storage devices.

This could prove a major boon to the use of solar, wind and other renewable energy sources. Because renewables produce electricity intermittently, integrating them into existing power grids is a significant challenge.

Storing the energy produced by solar, wind and other renewables would help balance the power going into the grid with the demand for power at any given time.

Liu and her colleagues have been trying for years to find the perfect material for using in energy storage devices called capacitors, which could help solve this problem.

In simple terms, you make a capacitor by separating two metal electrodes with an insulator, known technically as a dielectric material, Liu explains.

"If you have two coins that you put a piece of paper between, already you've made a capacitor -- but the paper has a very tiny energy storage capability."

The ideal material needs to meet three requirements: a very high dielectric constant, meaning it can store a lot of energy; a very low dielectric loss, meaning energy doesn't leak out and get wasted; and the capacity to work across a broad range of temperatures.

"It's a very big problem," says Liu. "Generally, if a material has a high dielectric constant, the energy loss is high and the temperature stability is very low."

Dielectric constant conundrum

Materials that have a high dielectric constant but also a high loss are basically useless because they don't store energy well, says co-author Professor Ray Withers, also from ANU.

Materials that only perform well at a certain temperature are also no good, because they cannot deal with normal daily temperature fluctuations.

But after five years of work, the researchers report that titanium dioxide manipulated at the molecular level appears to fit the bill perfectly.

"We believe this work breaks through the log-jam associated with the practical development of…materials for use in large capacitors and high-energy-density storage devices," they write in the journal Nature Materials .

The researchers found that titanium dioxide's dielectric constant is substantially higher than other materials, with excellent temperature independence and low levels of energy loss.

According to Liu, the material could be used in safe, solid-state 'supercapacitors' to store enormous amounts of energy, opening the door for innovation in the areas of renewable energy, electric cars, even space and defence technologies.

Abundant in Australia

Another plus for the material is its abundance. Titanium dioxide is found naturally around the world, and Australia already exports a significant amount.

"It's a very simple and abundant material," says Liu. "Australia currently dominates the market in this material."

Of course, the current research is only one step along the path to building functional capacitors using titanium dioxide, Liu notes.

"We've just developed the materials that have this potential, but we haven't developed practical applications."